On 15/02/18 13:06, Laurent Pinchart wrote:
> Hi Hans,
>
> On Thursday, 15 February 2018 13:56:44 EET Hans Verkuil wrote:
>> On 15/02/18 12:08, Laurent Pinchart wrote:
>>> On Thursday, 15 February 2018 12:57:44 EET Hans Verkuil wrote:
>>>> On 14/02/18 16:16, Laurent Pinchart wrote:
>>>>> On Wednesday, 14 February 2018 12:36:43 EET Niklas Söderlund wrote:
>>>>>> There is no way for drivers to validate a colorspace value, which could
>>>>>> be provided by user-space by VIDIOC_S_FMT for example. Add a helper to
>>>>>> validate that the colorspace value is part of enum v4l2_colorspace.
>>>>>>
>>>>>> Signed-off-by: Niklas Söderlund <niklas.soderlund+rene...@ragnatech.se>
>>>>>> ---
>>>>>>
>>>>>> include/uapi/linux/videodev2.h | 4 ++++
>>>>>> 1 file changed, 4 insertions(+)
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> I hope this is the correct header to add this helper to. I think it's
>>>>>> since if it's in uapi not only can v4l2 drivers use it but tools like
>>>>>> v4l-compliance gets access to it and can be updated to use this instead
>>>>>> of the hard-coded check of just < 0xff as it was last time I checked.
>>>>>>
>>>>>> * Changes since v1
>>>>>> - Cast colorspace to u32 as suggested by Sakari and only check the
>>>>>> upper boundary to address a potential issue brought up by Laurent if
>>>>>> the data type tested is u32 which is not uncommon:
>>>>>> enum.c:30:16: warning: comparison of unsigned expression >= 0 is
>>>>>> always true [-Wtype-limits]
>>>>>>
>>>>>> return V4L2_COLORSPACE_IS_VALID(colorspace);
>>>>>>
>>>>>> diff --git a/include/uapi/linux/videodev2.h
>>>>>> b/include/uapi/linux/videodev2.h index
>>>>>> 9827189651801e12..1f27c0f4187cbded 100644
>>>>>> --- a/include/uapi/linux/videodev2.h
>>>>>> +++ b/include/uapi/linux/videodev2.h
>>>>>> @@ -238,6 +238,10 @@ enum v4l2_colorspace {
>>>>>> V4L2_COLORSPACE_DCI_P3 = 12,
>>>>>> };
>>>>>>
>>>>>> +/* Determine if a colorspace is defined in enum v4l2_colorspace */
>>>>>> +#define V4L2_COLORSPACE_IS_VALID(colorspace) \
>>>>>> + ((u32)(colorspace) <= V4L2_COLORSPACE_DCI_P3)
>>>>
>>>> Sorry, this won't work. Use __u32. u32 is only available in the kernel,
>>>> not in userspace and this is a public header.
>>>
>>> Indeed, that I should have caught.
>>>
>>>> I am not convinced about the usefulness of this check either. Drivers
>>>> will typically only support a subset of the available colorspaces, so
>>>> they need a switch to test for that.
>>>
>>> Most MC drivers won't, as they don't care about colorspaces in most
>>> subdevs. It's important for the colorspace to be propagated within
>>> subdevs, and validated across the pipeline, but in most case, apart from
>>> the image source subdev, other subdevs won't care. They should accept any
>>> valid colorspace given to them and propagate it to their source pads
>>> unchanged (except of course for subdevs that can change the colorspace,
>>> but that's the exception, not the rule).
>>
>> Right. So 'passthrough' subdevs should just copy this information from
>> source to sink, and only pure source or pure sink subdevs should validate
>> these fields. That makes sense.
>>
>>>> There is nothing wrong with userspace giving them an unknown colorspace:
>>>> either they will map anything they don't support to something that they
>>>> DO
>>>> support, or they will return -EINVAL.
>>>
>>> The former, not the latter. S_FMT should not return -EINVAL for
>>> unsupported
>>> colorspace, the same way it doesn't return -EINVAL for unsupported pixel
>>> formats.
>>>
>>>> If memory serves the spec requires the first option, so anything unknown
>>>> will just be replaced.
>>>>
>>>> And anyway, this raises the question of why you do this for the
>>>> colorspace
>>>> but not for all the other enums in the V4L2 API.
>>>
>>> Because v4l2-compliance tries to set a colorspace > 0xff and expects that
>>> to be replaced by a colorspace <= 0xff. That seems like a bogus check to
>>> me, 0xff is as random as it can get.
>>
>> v4l2-compliance fills all fields with 0xff, then it checks after calling the
>> ioctl if all fields have been set to valid values.
>>
>> But in this case it should ignore the colorspace-related fields for
>> passthrough subdevs. The only passthrough devices that should set
>> colorspace are colorspace converter devices. I'm not sure if we can
>> reliably detect that.
>>
>>>> It all seems rather pointless to me.
>>>>
>>>> I won't accept this unless I see it being used in a driver in a useful
>>>> way.
>>>>
>>>> So for now:
>>>>
>>>> Nacked-by: Hans Verkuil <hans.verk...@cisco.com>
>>>
>>> Can you then fix v4l2-compliance to stop testing colorspace against 0xff ?
>>
>> For now I can simply relax this test for subdevs with sources and sinks.
>
> You also need to relax it for video nodes with MC drivers, as the DMA engines
> don't care about colorspaces.
Yes, they do. Many DMA engines can at least do RGB <-> YUV conversions, so they
should get the colorspace info from their source and pass it on to userspace
(after correcting for any conversions done by the DMA engine).
Regards,
Hans
